Method of preparing a sulphur containing compounding agent for rubber



COAUNG OR PLASHU Patented May 7, 1946 Examiner METHOD OF PREPARING ASULPHUR CON- 1 TAINING COMPOUNDING AGENT FOR RUBBER Fritz S. Rostler,Heinz W. Sternberg, and Hubert I. du Pont, Wilmington, Del., assignorsto Wilmington Chemical Corporation, Wilmington, Del., a corporation ofDelaware No Drawing. Application December 19, 1942, Serial No. 469,570

4 Claims.

The present invention relates to an agent useful in the compounding ofsynthetic rubber.

Yet more specifically the present invention is concerned with theprovision of a stable sulphurcarrying material having the property offacilitatmg the distribution of sulphur in synthetic rubber. Due to itshigh compatibility with synthetic rubber it may be readily compoundedwith those vulcanizable products which resist the dispersion of sulphur,particularly the present synthetic rubber-like materials of the Buna-Ntype. The product moreover contains sulphur in a form available forvulcanization. It has hitherto been almost universally the practice toadd the necessary sulphur for hot vulcanization in powdered elementalform. Few organic liquids contain or are capable of holding sulphur in acondition available for the desired action upon the rubber. Few organicsolvents have any substantial capacity for dissolving elemental sulphur.Moreover, the usual low boiling temperature of sulphur solvents rendersit impossible to utilize them in a compounded mass under elevatedtemperatures. Among other things a solvent volatile at vulcanizingtemperatures would expand, causing porosity in the vulcanizate.

It is now recognized that the uniform dispersion of elemental sulphur inthe present day synthetic rubbers represents a serious problem ofcompounding. Where dispersion of the solid material is incomplete it hasbeen found that the particles tend to agglomerate with the result thatthe final soft rubber resulting from vulvanization is non-uniform inproperties and therefore seriously impaired in over-all characteristics.In particular this difiiculty is characteristic of synthetic rubbers ofthe butadiene copolymer type and especially the so-called Buna-Nrubbers, formed by the copolymerization of butadiene and acrylonitrile.At the same time a similar difiiculty may be noted in the case ofsynthetic rubbers of other types which are not or are only difficultyplasticizable. This problem may be solved and the difficulty obviatedwhere the sulphur is introduced in homogeneous dispersion within anorganic carrier, as indicated in the copending application of 'FritzRostler, Serial No. 471.473, filed January. 6, 1943.

The manufacture of sulphur-carrying organic preparations having fluentto plastic properties suitable for the present purpose is impeded by thenecessity for observing many requisite factors. Thus, the proportion ofsulphur carried in form available for reaction with the synthetic rubbermust be sufllciently high with respect to the quantity of carrier whichcan be tolerated so as to completely satisfy the requirements of thevulcanizable constituents. Such a preparation moreover must benecessarily compatible with the synthetic rubber and preferablyrelatively fluent or plastic to permit ready compounding. Even an inertadditive would necessarily, in any substantial proportion, normally tendto impair the character of the final material and it is thereforedesirable that the carrier or organic solvent with which the sulphur isassociated be adapted to form a useful, cooperative ingredient in thefinal vulcanizate.

It is an object of the present invention to provide an organicvulcanizlng agent which is stable and which contains an adequately largeproportion of sulphur available in a form suitable for activevulcanization.

It is yet a more specific object achieved by the present invention toprovide a plastic and readily compatible preparation as above which,when employed in adequate proportion to effect vulcanization, does notimpair the character of the final vulcanizate, and in fact has theproperty of covulcanization with the rubber, probably through a sulphurbridge linkage. In short, the non-sulphur components or portions of thepreparation are not at all harmful to the final synthetic rubber and infact form an advantageous addition from the standpoint of extending,bulking, plasticizing and/or otherwise enhancing the use of thecompounded materials.

In accordance with the present invention there s employed a stablesulphur-containing preparation preferably formed from sulphur, and alargely unsaturated by-product of the petroleum industry havingcharacteristics substantially identical with those of the productsformed by neutralizing petroleum acid sludge and fractionating theorganic constituents thereof under vac uum to eliminate at least theportions boilin below C. and preferably outside the range from 160 to360 C. at 12 mm. Hg.

It has hitherto b. en proposed, as seen, for example U. S. Patent2,180,367, to employ such unsaturated materials as compounding agentsfor improving the properties of rubber. It ha been observed that thissubstance is a solvent for elemental sulphur in relatively smallconcentrations normally below about 4 per cent. Such concentrations are,however, obviously inadequate to permit its use as a sulphur carrier inthe compounding of synthetic rubber since the product itself isvulcanizable with from 3 to 6 per cent of the su1- phur and even anexcessive addition would normally be inadequate to satisfy the sulphurrequirements of the mixture. While its capacity for dissolving sulphurincreases somewhat at higher temperatures, separation tends to occur assoon as the temperature is lowered to normal. It is apparent thatutilization of such preparations on an industrial scale is thereforeimpractical.

In accordance with the present invention it has been discovered,however, that the fore aiedmcductmaxh ug w to form stable preparatiopfain' as w M 11 concentrations, for example, approaching in someinstances as misstatement, which preparations remain homogeneous and donot tend to separate or crystallize at atmospheric temperatures andwhich have advantageous properties enabling them to be readilycompounded with synthetic rubbers in relatively large proportion.

In fact, highly advantageous commercial vulcanizates may be preparedfrom mixtures containin to 50 per cent and hi her of theunsatl'eliedahadmnar. cncwitnout.imsweslthem synthetic uber.rulceniaawiaewx These preparations may be prepared within as wide arange of viscosity as desired, in accordance with the procedure observedduring their preparation. They accordingly may be pre-selected in regardto viscosity so as to greatly facilitate compounding.

More specifically it has been discovered that valuable sulphurcontaining compositions as above may be prepared by reacting excessquantitles of sulphur with the foregoing fractionated neutralizedpetroleum acid sludge products at temperatures substantially above themelting point of sulphur where I-IzS is liberated and for a suflicientperiod of time to assure the formation of a stable reaction product. Thereaction is advantflfifi. l and more ex editiousl carried outerelfilliamm m minimal lggiorgzlfiiwc. l. ower temper atu res may resultin an excessively prolonged reaction period.

At the reaction temperature a plurality of chemical effects are noticed.Thus the components of the mixture apparently react progressively toform the desired stabilized product. Concurrently therewith liberationof sulphur takes place in the form of H28, presumably as the result ofthe foregoing reaction. It is particularly important to note that therelative extent to which sulphur is liberated by this latter eifectaffords a valuable index as to the extent to which the formation of astabilized product is taking place in the reaction mixture. Conversely,the loss of sulphur as indicated by the sulphur content of the reactedproduct may be utilized as an indication of the extent to which thereaction has progressed.

More speglj llallxmtentimum $9.113 W rmall quateportion ofhxed sulpfiucom leted W en at sastamutlmncenteisulrb r based onitlie final product,is lost from the reac ion It is to be noted that the percentage ofsulphur 101% above is, for convenience, expressed on the basis of thefinal sulphur-hydrocarbon product.

The foregoing principles apply in general, irrespective of the amount ofsulphur in the final reaction product. In other words, regardless of theproportion of sulphur originally added or fixed in stable form, thereaction is normally complete when the proportion of sulphur loss fallswithin the range heretofore stated. In this way stable homogeneouscomposition containing as high as 35 per cent sulphur may be prepared.These result, for example, from reacting an admixture containing about40 per cent sulphur and approximately per cent of the sludge distillateat a sufficiently elevated temperature and for a sufiicient period oftime until loss of sulphur amounts to, at least, from 5 to '7 per centby weight of the final product. The final preparations, having lowersulphur content, however, may be prepared and in fact are much moreadvantageous for commercial purposes. The range of utility seems toextend from 35 per cent of fixed sulphur substantially down to thatproportion of sulphur which is normally soluble in the distillate atroom temperature. News, as oa 0.,- o poucts con ainin substantiallyabove the 4 per Wphu; ngriafii solubmig temp''r' at'ure and pre erablyabove 5 per cenkglt hp gh suWer ranging,

W viscosit increase sirsnteaecusmam misi at e l e ,visc, si qf the artimaterial and in the case of the. preferred iedllrdre nmaesiiuae.mrm= inge o tiii'iuiii base material a final yiscpsityofutest....aliQut.-..lQQ..;.centinaises..isadmirablemii'it urT while thisis an optimum figure which is advanced for illustrative purposes andwhich may be varied materially, nevertheless it represents what isprobably a close approximation of completion of the reaction. Thesulphur los may be permitted to proceed to higher degree and to as greatan extent as desired although at losses greater than '7 per cent nonoticeable advantage ensues and the reaction product may assume anexcessive increase in viscosity. The process may 1 om te minated umappearance of as little as about 5 per cent of 76 Usually a producthaving such viscosity characteristics results when the sulphur loss hasbeen carried to the extent indicated above.

In view of the difiiculty of specifically standardizing the product bycontrolling the reaction it is advisable to prepare products of a highersulphur content and, if necessary, adjust them to the desiredconcentration by diluting back with some of the original distillate. Theproduct is not at all impaired by such dilution and, starting withhigher concentration of fixed sulphur, products containing 8, 10 and 15per cent sulphur may be provided which are stable in storage and can beincorporated hot or cold into a. rubber mixture.

, a complex in structure, and weakly MMW y ow odih'e fi'umbers which areCOATING OR PLASTlC are much more viscous than the normal petroleum oilsfrom which they are separated during the refining treatment. wenezgllyhaye thg w meuawaaeailreflgem; ii...9fl.9.ehashsbtlaiiuic.resin- Theythus form plastic materials which are readily compatible with syntheticrubber and apparently covulcanize with the synthetic rubber. In short itappears that the products during vulcanization become bound to therubber molecule by bridge linkages over the sulphur atoms.

This unsaturated h teearbe. mate ial. sal characieuzea' isolu fiitr, .nr all organic so liiiiits," andl' 'ibiy ubstantial solubility in strongl2.ll!l&e9.isla. udin nconcentr d, fu n..ng' acid. It generally notreactive'wit-h dilute reagents, but it reacts with many concentratedreagents. It is capable of an extensive reaction with sulphur, which issimilar to caoutchouc vulcanization. It is also capable of nitration,and of polymerization and condensation with the ingredients of varioustypes of synthetic resins.

As startin ,F. E. used e e lzl rsnaas 'FJEEQJLQMLEQQ muaitherelmaymbeJud es. which .are

orm 111 1119.!SEQQZQSQQi-miiziial-o l products w or the residuesobtaingg in o nets with various selective sglygnts, ng;

cresol, i ichlor-diethy1 her, an 1' 1d 2..' I

ad: in b .9 Useful procedures for production of the desired unsaturatedhydrocarbon materials are disclosed in considerable detail elsewhere.For example, U. S. Patents Nos. 2,185,951, 2,185,952 and 2,217,918, aswell as application, Serial No. 227,862, now U. S. Patent No. 2,247,411,describe various methods of obtaining the desired unsaturatedhydrocarbon materials from acid sludges and from the residues of solventrefining. The hydrocarbons lemalmescribgiln nsleedeiaunndrlaimedriflaieiaet 2,217,919. Briefly stated, thesehydrocarbon mateam are generally obtained by distillation under vacuumof solvent extract residues or the organic constituents of acid sludgesor selected portions thereof. This distillation is generally effected inthe presence of alkaline reagents or after thorough neutralization ofthe starting material with alkali, and the recovered material generallyhas a boiling range between 160 and 380 C. at an absolute pressure of 12mm. Hg. Usually the material is recovered in fractions having narrowerboiling ranges. For general use in accordance with the present inventionthe upper limit of boiling range is not particularly critical but it isadvantageous to eliminate all fractions boiling below about 160 C. at 12mm. Hg.

As will be apparent from the foregoing, the present inventioncontemplates, in accordance with its preferred embodiment, thesulphurization of certain unsaturated hydrocarbon distillates derivedfrom the refining of mineral oil, and which are rendered suitable forthe present purposes by elimination of certain fractions which tend toimpair the utility of the final product for the present purposes. Inshort, the removal by ixtures of uding fgrfwl, phenol rxaminet RE EQLZLELBEQEBQES.rihiqlllllay.l9e.ileeieq i a 'le f the presentincordance withthe r vgnggn- 0 t talcum.-. ing from cracking or those contai ng a ng tgra lly high cggfimn lllllmtlwatfi Sffcn productsgnay ificludeasph'altig petrolgpm roducts as well as pitu mln o ys prodg gts such agcal'tar and related. asphalts and the natura asphalts such gsgigsonitg, As is apparen 1'0 e m e invention thus contemplates theutilization of undistilled extracts as well as neutralized acid sludgesof suitable viscosity and boiling point. Pine tar similarly has someutility in accordance with the present invention. In general thesematerials are suitable for treatment in accordance with the principleshereinabove enunciated, provided that they possess a boiling pointsubstantially above C. at 12 mm. Hg and contain a substantial proportionof unsaturated material. More specifically the boiling point should beconsiderably in excess of 160 C. at 12 mm. Hg and preferably above 130or C. at 12 mm. Hg. The requisite degree of unsaturation is indicatedconveniently by solubility in sulfuric acid both concentrated andfuming. Hydrocarbon tars and asphalts of the required boiling point andsoluble at least to the extent of 40 per cent in fuming sulfuric acidall seem to possess utility for the present purposes. It will beappreciated, however, in view of the principles stated above "that a.larger proportion of unsaturates is to be preferred, the foregoingrepresenting an approximate minimum of the operative range of utility.Higher concentrations of unsaturated material are increasinglyadvantageous as are also higher boiling materials in so far as the finalmaterial can be incorporated in higher proportions to give anadvantageous degree of fluidity for facilitating incorporation of otheringredients, such as powdered fillers, into the rubber mix. It has beenfound important that the hydrocarbon base used in the production ofthese sulphur preparations should consist mainly of unsaturated materialbut the unsaturation should not be too high because highly unsaturatedproducts impart bad ageing properties and brittleness to the finalvulcanizate. Compositions having an iodine number between 20 and 60 andpreferably between 40 and 60 have been found most suitable and materialof this kind can be incorporated into synthetic rubber compounds in verylarge amounts without impairing their physical properties or ageincharacteristics. The most suitable source for these hydrocarbonmaterials are the above-described waste products of mineral oilrefining.

It is thought pertinent to point out that various sulfurized materialshave hitherto been proposed as extreme pressure and cutting oilingredients for use in lubricating oils. It has been suggested toutilize starting materials comprising the extracts from solvent refiningof mineral lubricating oils. In general, however, these products containa low sulfur concentration, particularly in combination with the finaloil and in no proposal with which we are aware is there any suggestionof producing products containing relatively high concentrations of fixedsulphur, in accordance with the principles enunciated above for thepurpose of producing a product compatible and co-vulcanizable withsynthetic rubber and wherein the sulphur is in the form available forsatisfying the requirements of the vulcanizable components of the mix.

The following are a few specific examples, given for purposes ofexemplifying optimum procedure in accordance with the present invention:

Example 1.85 parts by weight of a distilled hydrocarbon" materialobtained from the neutralized acid sludge formed in the refining ofmineral lubricating oil and having a boiling range of 250 to 360 C. at12 mm. Hg were admixed with 15 parts of finely divided sulphur. Themixture was heated to 190 C. and held at this temperature for fourhours. At the end of this period the product containing 9 per centsulphur, available for vulcanization, was cooled. The sulphur content ofthe finished product as referred to the original mixture amounts to 8.4parts. The loss accordingly was equal to 6.6 parts of the originalmixture and thus equal to 7 per cent on the final product.

The product was a stable, homogeneous, readily flowing, plastic materialhaving a viscosity of approximately 200 centipoises at 100 C. It may bediluted with sufiicient proportion of the original unreacted hydrocarbonto bring the final admixture to a sulphur concentration of 6 or 8 percent as desired. suitable as a sulphur carrier which is particularlyadvantageous in connection with the compounding of synthetic rubbersnotably of the Buna-S and Buna-N type. Various other time andtemperature relations may be resorted to in order to produce analogousproducts. Thus at a reaction temperature of 215 C. the foregoing mixturemay result in a suitable preparation containing 8.6 per cent sulphur in30 minutes. The product possesses a viscosity of 110 centipoises at 100C. Additional heating results in somewhat of an increase in viscosityand a lowered final sulphur content.

At lower reaction temperatures, such for example as 180 C., longer timeof treatment is required. Utilizing the starting mixture containing 15per cent sulphur, six hours heating time is normally necessary andresults in a product containing 8.8 per cent sulphur and having aviscosity of 186 centipoises at 100 C.

Example 2.80 parts by weight of distilled hydrocarBon material derivedfrom the solvent extract refining of mineral oil and having a boilingrange of from 240 to 280 C. at 12 mm. Hg were mixed with 20 parts byweight of finely divided sulphur. The mixture was heated to 180190 C.and held within this range for four hours. At the end of this time thereaction product had a sulphur content of 13 per cent, representing asulphur loss of 8.8 per cent based on the final total composition.

Sufiicient additional unreacted hydrocarbon distillate may beconveniently added to standardize the composition at a fixed sulphurcontent of per cent. Advantageously the ingredients are warmed to about140 C. to promote admixture. The resulting product is quite stable underall conditions of storage.

Example ,75 parts of an unsaturated hydrocar on distillate as above aremixed with 25 parts of sulphur and heated to 215 C. for one hour. Theresulting product is a stable product of particular utility in thecompounding of Buna-N type rubber, having a sulphur content of 14.9 percent.

Where the heating period is shortened to 30 minutes the product contains17.6 per cent sulphur in fixed form, Prolonged heating for 6 hoursresults in a quite viscous material containing 8.2 per cent sulphur.

What we claim is:

1. A method of preparing a viscous liquid to plastic compositioncompatible with synthetic rubber and containing between 5 and about 35%sulphur based on the weight of the composition and in a form availablefor vulcanization, said composition being stable as to separation andcrystallization of sulphur at atmospheric temperatures; comprisingreacting an amount of sulphur at least 5% in excess of the sulphurdesired in the final composition and an unsaturated hydrocarbon masshaving approximately of carbon and 10% of hydrogen and substantiallyfree of fractions having a boiling point of less than about 160 C. at 12mm. Hg, of the class consisting of components derived from the extractseparated in the solvent refining of mineral oils and componentsseparated by the distillation of neutralized acid sludge of petroleumoil refining, said reaction utilizing a temperature substantially abovethe melting point of the sulphur and at which H2S is evolved from saidreactive components, said reaction being carried out for a time not lessthan that necessary to volatilize at least 5% of the sulphur based onthe weight of the composition.

2. A method of preparing a viscous liquid to plastic compositioncompatible with synthetic rubber and containing between 5 and about 35%sulphur based on the weight of the composition and in a form availablefor vulcanization, said composition being stable as to separation andcrystallization of sulphur at atmospheric temperatures; comprisingreacting an amount of sulphur at least 5% in excess of the sulphurdesired in the final composition and an unsaturated hydrocarbon masshaving approximately 90% of carbon and 10% of hydrogen and having aboiling point range of between about 190 C. and 360 C. at 12 mm. Hg, ofthe class consisting of components derived from the extract separated inthe solvent refining of mineral oils and com: ponents separated by thedistillation of neutralized acid sludge of petroleum oil refining, saidreaction utilizing a temperature substantially above the melting pointof the sulphur and at which H28 is evolved from said reactivecomponents, said reaction being carried out for a time not less thanthat necessary to volatilize at least 5% of the sulphur based on theweight of the composition.

3. A viscous liquid to plastic composition compatible with syntheticrubbers and containing between 5 and about 35% sulphur based on theweight of the composition and in a form available for vulcanization,said composition being stable as to separation and crystallization ofsulphur at atmospheric temperatures and having a viscosity in excess ofcentipoises at 100 C., said composition comprising the reaction productof an unsaturated hydrocarbon mass having approximately 90% of carbonand 10% of hydrogen, and substantially free of fractions having aboiling point of less than about C. at 12 mm. H of the class consistingof components derived from the extract separated in the solvent refiningof mineral oils and components separated by the distillation ofneutralized acid sludge of comma OR PLASTIC petroleum oil refining, andan amount of sulphur equal to at least 5% in excess of the sulphurcontained in the final composition, said reaction being carried out fora time not less than that necessary to volatilize at least 5% of thesulphur based on the weight of the composition.

4. A viscous liquid to plastic composition compatible with syntheticrubbers and containing between 5 and about 35% sulphur based on theweight of the composition and in a form available for vulcanization,said composition being stable as to separation and crystallization ofsulphur at atmospheric temperatures and having a viscosity in excess of100 centipoises at 100 C., said composition comprising the reactionproduct of an unsaturated hydrocarbon mass having aptxaminez proximately90% of carbon and 10% of hydrogen, said unsaturated hydrocarbons havinga boiling point range between about 190 C. and 360 C. at 12 mm. Hg, ofthe class consisting of components derived from the extract separated inthe solvent refining of mineral oils and components separated by thedistillation of neutralized acid sludge of petroleum oil refining, andan amount of sulphur equal to at least 5% in excess of the sulphurcontained in the final composition, said reaction being carried out fora time not less than that necessary to volatilize at least 5% of thesulphur based on the weight of the composition.

FRITZ S. ROSTLER.

HEINZ W. STERNBERG.

HUBERT I. no PONT.

